Encapsulating compositions are often used to provide a barrier to contaminants. Encapsulants are typically used to encapsulate a device, such as a splice between one or more conductors, through which a signal, such as an electrical or optical signal, is transmitted. The encapsulant serves as a barrier to fluid and non-fluid contamination. It is often necessary that these devices, particularly splices, be re-entered for repairs, inspection or the like. In this use and others, it is desirable that the encapsulant be non-toxic, odorless, easy to use, transparent, resistant to fungi, and inexpensive.
Signal transmission devices, such as electrical and optical cables, typically contain a plurality of individual conductors, each of which conduct an electrical or optical signal. A grease-like composition, such as Flexgel, (commercially available from AT & T) is typically used around the individual conductor. Other filling compositions include petroleum jelly (PJ) and polyethylene modified petroleum jelly (PEPJ). For a general discussion of cable filling compositions, and particularly Flexgel type compositions, see U.S. Pat. No. 4,259,540.
When cable is spliced it is often the practice to clean the grease-like composition from the individual conductors so that the encapsulant will adhere to the conductor upon curing, preventing water or other contaminants from seeping between the conductor and the encapsulant. Therefore, an encapsulant which will adhere directly to a conductor coated with a grease-like composition is highly desirable.
Many of the connecting devices (hereinafter connectors) used to splice individual conductors of a cable are made from polycarbonate. A significant portion of prior art encapsulants are not compatible with polycarbonate, and thus, stress or crack connectors made from this material over time. Therefore, it is desirable to provide an encapsulant which is compatible with a polycarbonate connector.
Many of the prior art encapsulants, which have addressed the above problems with varying degrees of success, are based on polyurethane gels. Various polyurethane based gels are disclosed in U.S. Pat. Nos. 4,102,716; 4,533,598; 4,375,521; 4,355,130; 4,281,210; 4,596,743; 4,168,258; 4,329,442; 4,231,986; 4,171,998; Re 30,321; 4,029,626 and 4,008,197. However, all of the polyurethane gels share at least two common problems. It is well known in the art that isocyanates are extremely reactive with water. The above polyurethane systems utilize two part systems which include an isocyanate portion and a crosslinking portion designed to be added to the isocyanate when it is desired that the gel be cured. Because of the water reactivity of isocyanates, it has been necessary to provide involved and expensive packaging systems to keep the isocyanate from reacting with water until such time as the isocyanate can be cured with the crosslinking agent.
Further, it is well known in the art that isocyanate compounds are hypo-allergenic, and thus, can induce allergic reactions in certain persons. This is of particular concern when a two part systemis used which requires a worker to mix the components on site.
Therefore, it is highly desirable to provide an encapsulant which may be used in conjunction with a signal transmission device as a water-impervious barrier, which has good adhesion to grease-coated conductors, which is compatible with polycarbonate splice connectors, and which does not require the use of an isocyanate compound.